1. Technical Field of the Invention
This invention relates generally to wireless communications systems and more particularly to radio receivers used within such wireless communication systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), radio frequency identification (RFID), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, RFID reader, RFID tag, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system or a particular RF frequency for some systems) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier (LNA) receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
For a receiver to reliably recover data from received inbound RF signals it must be able to isolate desired signal components of the inbound RF signals from interferers (e.g., interference from adjacent channel(s), interference from other devices and/or systems using frequencies near the frequency band of interest, and/or transmission blocking signals that occur in RFID systems). For example, in a cellular system, it is fairly common to have significant nearby interferers of the frequency band of interest (e.g., one or more desired channel(s) of 5-60 MHz centered at a frequency of about 900 MHz, 1800 MHz, 1900 MHz, and/or 2100 MHz) that adversely affect the ability of a receiver to accurately recover data.
One solution to reduce the adverse effects caused by interferers is to use an off-chip band pass filter (BPF) prior to the LNA to attenuate the interferers and pass the desired channel(s). However, with nearby interferers (e.g., within 100 MHz), the BPF needs a steep roll off to sufficiently attenuate the interferers making it an expensive part. In addition, an off-chip BPF typically reduces the magnitude of the desired channel(s) by about 3 dB. Another solution is to use a less expensive BPF with less roll off. While this reduces the cost and the attenuation of the desired channel(s), it does not sufficiently attenuate large nearby interferers.
A further issue with interferers is that their harmonics may also adversely affect the ability of a receiver to accurately recover data. For instance, while the receiver may adequately attenuate the interferer and pass the desired channel(s), the interferer harmonics may propagate through the receiver providing a high frequency noise that adversely affects high speed functions of the receiver (e.g., baseband operations, analog to digital conversion, etc.).
Therefore, a need exists for a radio receiver that sufficiently attenuates harmonics of interferers (which includes blocking signals) with negligible attenuation of the desired channel(s).